The present invention relates to ink jet recording. More particularly, the present invention relates to a coated sheet, and in particular a coated paper, which is suitable as a recording sheet for use in an ink jet recording process.
Ink jet recording systems are now widely known. They generate almost no noise and can easily perform multicolor recording. Generally, the recording sheets used in ink jet recording processes today are coated sheets, and in particular coated papers. Typical coatings applied to ink jet recording papers utilize high levels of small particle size silica. The use of the silica aids in absorbing ink, thereby permitting the high speed nature of the ink jet printing to occur. The ink jet inks are mostly water based with water soluble dyes providing the print color.
The silica used in ink jet recording papers, generally have surface areas above 200 m.sup.2 /g as measured by the BET method. See, for example, U.S. Pat. No. 4,478,910, which discloses an ink jet recording paper comprising a base sheet with a specific sizing degree, a coating layer comprising a water soluble polymeric binder and a particular fine silica particle. The use of such silica, however, is difficult to formulate into coating formulations due to its affect on rheology. Typical silica coating formulations generally comprise from 15 to 50% by weight solids.
Furthermore, although silica systems provide excellent ink jet recording materials, they do have limitations in terms of dusting due to their high binder demand. They also generally provide a matte finish instead of glossy surfaces, and current systems produce limited dot size. Dot size will need to be reduced with higher resolution printers becoming more available, which is a trend in the graphic arts industry.
Coated ink jet papers employing various polymers are also known.
For example, in U.S. Pat. No. 4,481,244, an ink jet recording material is described which comprises a substrate and a coating layer formed of a polymer having both hydrophilic segments and hydrophobic segments. Such a polymer is prepared by addition-polymerizable vinylic monomers. Hydrophilic segments comprising carboxylic or sulfur groups, or ester groups thereof are introduced into the polymer by using a prescribed amount of an alpha, beta unsaturated monomer such as acrylic acid, methacrylic acid, crotonic acid, itaconic acid, maleic acid, fumaric acid, vinylsulfonic acid, sulfoethylmethacrylate, sulfopropylmethacrylate or sulfonated vinyl naphthalene. Monomers most suitable for introducing the hydrophobic segments are styrene, styrene derivatives, vinyl naphthalene, vinyl naphthalene derivatives and esters derived from aliphatic C.sub.8 -C.sub.18 aliphatic alcohols and alpha, beta ethylenic unsaturated carboxylic acids. Once the polymer has been prepared from a combination of the required monomers, it is necessary to form a salt of the polymer in order to make the polymer soluble or colloidally dispersible in the medium of the coating material. Substances which can combine with the polymer to form the salt include alkali metals such as sodium and potassium, as well as aliphatic amines.
U.S. Pat. No. 4,425,405 discloses an ink jet recording sheet comprising a paper support and a coating composition which comprises an aqueous dispersion of polyvinylpyrrolidone, vinyl pyrrolidone-vinyl acetate copolymer or a mixture thereof serving as a binder or sizing agent, and a white filler. The patent also discusses other systems known to the art which involve the use of sizing agents. Such sizing agents include oxidized starch, polyvinyl alcohol, galactomannon gum, polyacrylamide, sodium alginate, styrene-maleic acid copolymer, carboxymethyl cellulose and other cellulose derivatives, casein, soy bean protein and the like. The use of sizing additives, such as hydrophobic materials or latices, rosins and its derivatives, petroleum resins, fumaric acid, maleic acid and its derivatives, waxes, synthetic resins, fatty acids, alkyl ketene dimers and the like, are also mentioned. The use of systems comprised of a white pigment such as clay, talc, diatomaceous earth, calcium carbonate, calcium sulfate, barium sulfate, titanium oxide, zinc oxide, zinc sulfide, satin white, aluminum silicate, lithopone and the like in combination with a binder resin, such as oxidized starch, etherified starch, gelatin, casein, carboxy methyl cellulose, hydroethyl ethylcellulose, polyvinyl alcohol and SBR latex, are also briefly discussed.
U.S. Pat. No. 4,371,582 describes an ink jet recording sheet containing a basic latex polymer. As described in the examples, formulations comprised of the basic latex can be coated onto a sheet and dried to provide an ink jet recording sheet, or impregnated into the sheet to provide an ink jet recording sheet. The dyes useful with the basic latex are described as being any water-soluble dyes having at least one sulfo group in the molecule.
U.S. Pat. No. 4,496,629 relates to a recording paper characterized by comprising a substrate coated with a layer finely divided by microcracks of irregular form into numerous lamellae. The coating layer is basically comprised of a material which contains a film formable resin, and which may additionally contain one or more components selected from various surfactants and porous inorganic powders. Either water soluble resins or organic solvent soluble resins are usable. The paper quickly fixes a coloring matter of ink by capturing it with the lamellae and also quickly absorbs the solvent of the ink through the microcracks into the substrate.
U.S. Pat. No. 5,215,812 discloses a coated printing paper which comprises a paper substrate, a pigment coated layer on one or both sides of said substrate, and superposed thereon a surface layer of a thermoplastic polymeric latex having a second order transition temperature of at least 80.degree. C. The surface layer is treated with a calendar at a temperature less than said second order transition temperature in order to prepare a high gloss layer.
The use of polymer based ink jet coatings, however, have always experienced problems with regard to ink absorptivity. Thus, immediately after recording, the dried state of ink is actually unstable and this results in inherent problems when sheets just after recording are contacted under pressure or stacked upon high speed recording. The result is that the ink migrates or is scratched upon transfer of the still unstable imaged sheets on the roll of the recording apparatus. This is one of the reasons that silica systems are primarily used today. Nevertheless, as discussed above, silica systems also have limitations.
It is therefore an object of the present invention to provide a system which avoids the problems of using silica.
Another object of the present invention is to provide a system based upon a polymer which exhibits excellent affinity for ink jet inks.
It is yet another object of the present invention to provide an ink jet paper comprised of high binder levels resulting in improved coating strength.
Still another object of the present invention is to provide an ink jet recording paper which exhibits high definition, contrast, improved dot size and improved gloss.
These and other objects and aspects of the present invention will become apparent to one skilled in the art upon a review of the following description and the claims appended hereto.